It is known to use charging devices in electrophotographic printing. Such charging devices are typically of the following types: corotron, dicorotron, pin corotron, scorotron, discorotron, and pin scorotron. See, generally, R. M. Schaffert, "Electrophotography," The Focal Press, New York, 1965.
As known, such charging devices include a chamber arranged with a charge-generating element such as, for example, a wire, a dielectric wire, or a pin array. As part of the charge-generating process, however, unwanted gases such as nitrous oxide and ozone are generated in the chamber. Some problems associated with these unwanted gases in charging devices are discussed in Louis Reale, U.S. Pat. No. 4,585,322 at col. 2-3, and in Joseph H. Lang et al., U.S. Pat. No. 4,792,680 at col. 1-3.
To provide for proper operation of the charging device, therefore, it is desirable to arrange the charging device to facilitate the evacuation of such gases from the chamber.
To evacuate unwanted gases from the chamber, existing charging devices typically arranged with a single inboard-end vacuum arrangement that results in a large inboard-to-outboard flow gradient that requires substantial flow rates for emissions removal. This existing technology leads to non-uniform vacuum gradient that is higher at the outboard side. Also, this existing technology leads to the introduction of airborne contaminants resident inside the host printing or copying machine. Computed flow fields for a typical charging device using this single-end vacuum arrangement show velocity gradients of 2 to 3.times. from inboard to outboard. Due to the non-uniformity of the vacuum air flow, high flow rates are required to effectively remove ozone over the entire length of the device. Even at these high flow rates, greater than 3 cubic feet per minute ("CFM"), it is not guaranteed that the induced flow will overcome the effect of corona wind.
As a result, it is desirable to provide an improved charging device.